1. Field of the Invention
The present invention relates to an image processing apparatus and method for performing color correcting according to environment light, a storage medium for storing the image processing method, and an environment light measurement apparatus for measuring the environment light.
2. Related Background Art
In recent years, since color image products are widely used, a color image can be easily managed not only in a specific field such as a design production field or the like using CG (computer graphics), but also in general office. In a any case, in a case where the image formed on a monitor is outputted by a printer, since a color of the monitor image does not coincide with that of the printed image, it is difficult to perform color checking of the printed image on the monitor. Therefore, as a method to solve such a problem, a color management system has been created and remarked.
The color management system is a system for eliminating a difference in color of each device by using a common color space. This system is based on an idea that, if the colors are represented by the same coordinates in the same color space, their manifestation (or appearance) is identical. That is, in this system, all the colors are represented in the same color space and their corresponding coordinates are coincided with others to obtain coincidence in the manifestation of color. At present, as one of such systems generally used, there is a method in which the difference in color of each device is corrected by using a CIE-XYZ color space as the color space, and by using XYZ tristimulus values which are internal description coordinate values of the CIE-XYZ color space.
Hereinafter, the environment for observing the image will be explained with reference to FIG. 28. FIG. 28 shows a case where an image which is the same as printed matter 201 is displayed on a monitor 203. In this case, ambient light 204 when the image is being observed is detected by an ambient light sensor 206 mounted on the monitor or the printer.
For example, the printed image or the image displayed on a CRT is not always observed in the fixed ambient light, but the ambient light 204 in FIG. 28 varies according to an environmental situation. Further, even if color coincidence can be obtained in one ambient light, when such ambient light varies, color-coincided images come to be seen as the images completely different from others. As shown in FIG. 27, in order to eliminate this, by using the above color management system, it is predicted on the basis of ambient light-information 108 previously obtained by a sensor 109 what value (e.g., XYZ values) the respective images have when these images are observed in one environment. Then, these predicted values are reproduced as faithfully as possible by using profiles 103 and 104 for respective devices, whereby it intends to coincide the manifested color with others.
Such a conventional example will be explained hereinafter with reference to FIG. 27. Initially, an input image (i.e., printed matter) is read by a scanner 101. Then, in a scanner RGB to XYZ conversion unit 102, R1, G1 and B1 signals obtained from the scanner 101 are converted into color signals X1, Y1 and Z1 not depending on any device, by using the scanner profile 103 in which previously provided scanner characteristic data has been stored. Further, in a signal conversion unit 104, on the basis of the ambient light information 108 obtained from the sensor 109 for sensing the ambient light, the signals X1, Y1 and Z1 are converted into color signals X2, Y2 and Z2 of each color in case of observing in such ambient light. Then, in an XYZ to monitor RGB conversion unit 105, monitor input values, i.e., R2, G2 and B2 signals, are calculated by using the monitor profile 106 and inputted to the monitor 107.
In the above conventional method, if the two colors have the same value in the common color space, they should be seen as the same. However, in a case where the color displayed on the monitor is compared with the color obtained by illumination (e.g., color on printed matter), it has been conventionally known that, even if these two colors have the same value, they can not be seen as the same by an observer. For this reason, in order to perceive or observe these two colors as the same by the naked eye in the above environment, further correcting is necessary.
In case of the printer, the profile can be obtained by adding various image data to the target device, measuring the color of the output image from the target device, and forming a table in which the various image data respectively correspond to the color-measured values. However, since it is assumed that environment illumination light in case of forming the profile has a value of standard illumination light which is determined by CIE and has spectral intensity as shown in FIG. 16, color change ratio of the CRT becomes different from that of the printed matter if the environment illumination light varies, whereby the colors on the CRT and the printed matter are observed as being different from each other. Therefore, in case of performing strict color matching, it is necessary to make the standard illumination light and the environment illumination light substantially the same when the profile is formed, and to measure a kind of the environment illumination light to further add a color correction process.
In case of observing colors, it is thought that a human being considers white as a standard color and thus recognizes all colors by comparing them with white. In this connection, it will be thought an example that a displayed image on a monitor and an image on printed matter both placed in one ambient light (i.e., environment light) are observed.
In such environment, there are many colors which are considered (or can be perceived) as white, e.g., white on the monitor, white in illumination light, white in an image (or paper) illuminated by the illumination light, and the like.
In a case where there are many colors which can be perceived as white in observation environment, an observer in such environment obtains the white acting as the standard when observing the color, by collecting perception as to the above-described whites in the many environments (i.e., white on the monitor, white in illumination light, white in an image (or paper) illuminated by the illumination light, and the like). At this time, the white perceived on the printed matter (i.e., white of the image (or paper) illuminated by the illumination light) and the white on the monitor highly affect the case of obtaining the standard white by collecting the perception, as compared with another white. For this reason, even if the identical illumination light is used, if the white (i.e., chromaticity value) of the paper used when obtaining the printed matter (i.e., hard copy) differs, also the standard white when observing the color highly differs.
Therefore, an object of a first invention is to realize highly accurate matching by performing color signal converting on the basis of the white of a recording medium and the white of the environment light.
In order to achieve the above object, the first invention provides an image processing method for performing the color signal converting on image data to make identical of color sight on a displayed image and color sight on an image formed on the recording medium, comprising the steps of:
obtaining information as to the white which is perceived on the formed image illuminated by the environment light, on the basis of information as to the recording medium and information as to the image processing environment light; and
performing the color signal converting by using the information as to the white obtained in the obtaining step and the information as to the white on a display device.
Further, the paper or ink which is the base material of the output printed matter tends to use a fluorescent whitening agent to improve a coloring characteristic. For this reason, e.g., as shown in FIG. 12 which illustrates a change in reflectance on the paper with UV-range (ultraviolet-range) illumination intensity, if the UV-range illumination intensity increases, the reflectance exceeds 100% in a partial wavelength (i.e., color) range due to fluorescent whitening effect, whereby the coloring characteristic varies.
Therefore, an object of a second invention is to be able to produce a high-quality output image by performing a correction process which takes into consideration the fluorescent whitening effect according to the UV-range illumination intensity.
In order to achieve the above object, the second invention provides an image processing apparatus comprising:
illumination light measurement means for measuring the illumination light, the means being composed of an optical sensor for measuring the UV-range illumination intensity and an optical sensor for measuring visible-range illumination intensity; and
correction process means for performing the correction process on the image data to correct the fluorescent whitening effect on the recording medium in accordance with a measurement result of the measurement means.
In the conventional method where environment illumination light under which the observing is performed is measured and the color correcting is performed, as shown in FIG. 26, such measuring is performed by a light sensor which has three-color, R (red), G (green) and B (blue) sensitivity of visible-range light (i.e., wavelength 380 to 780 nm), to judge color temperature and the environment illumination light thereby performing the color correcting. However, in such conventional method to measure and correct the color temperature with the three colors, there is a problem that such method can not be applied to a fluorescent lamp of which color rendering is deteriorated due to influence of a luminescent line or to a light source in which the fluorescent lamp and other lamps are mixed. For example, as shown in FIG. 12, if such illumination light which can be frequently seen in an office is measured in a spectral method, the influence of external light and the luminescent line clearly appears. Such influence could not be eliminated only by detecting a flicker and the luminescent line of the fluorescent lamp. Further, according to the measuring by the light sensor of the three colors including the luminescent line, a wavelength output of the luminescent line is large, whereas other wavelength outputs are relatively small. Thus, it is difficult to accurately measure the change in the illumination light in which the external light is included. For this reason, it has to use the spectral measurement method having loads in time and cost.
Therefore, an object of a third invention is to be able to accurately identify, with simple structure, the environment illumination light without the influence of the luminescent line of the light source.
In order to achieve the above object, the third invention provides an image processing apparatus comprising:
environment illumination light measurement means which is composed of a shorter-wavelength light detection unit having sensitivity in a wavelength band in which a peak of a main spectral sensitivity characteristic does not coincide with a peak of a main luminescent line of the fluorescent light, and a longer-wavelength light detection unit having sensitivity at a point where the spectral sensitivity characteristic corresponds to red; and
environment illumination light identification means for identifying environment illumination light by using a signal from the environment illumination light measurement means.
Further, in the conventional method where the environment illumination light under which the observing is performed is measured and the color correcting is performed, as shown in FIG. 26, such measuring is performed by the light sensor which has the three-color, R, G and B sensitivity of visible-range light (e.g., wavelength 380 to 780 nm), to judge the color temperature and the environment illumination light, thereby performing the color correcting. However, in such conventional method to measure and correct the color temperature with the three colors, since a wavelength range to be detected is wide, there is a problem that the fluorescent lamp or the like having the luminescent line can not be discriminated as the light source.
For this reason, in an improved conventional method, the luminescent line and the flicker are detected to judge whether or not the environment illumination light is the fluorescent illumination light. However, the illumination light which can be frequently seen in the office is the various light including the fluorescent lamp and other light source. For example, as shown in FIG. 24, if such environment illumination light is measured in the spectral method, the influence of the luminescent line clearly appears in the external light, whereby such environment illumination light is erroneously judged as the fluorescent illumination light.
In this case, however, if the environment illumination light is considered as the fluorescent illumination light and thus the color image process is performed, the reproduction color is incorrect. Further, according to a kind of the fluorescent lamp and a time elapsing for use of the fluorescent lamp, the color rendering differs. For this reason, in case of performing the accurate color reproduction, it had to use the spectral measurement method having the loads in time and cost.
Therefore, an object of a fourth invention is to be able to easily and highly accurately obtain the color rendering of the environment light which affects the color reproduction.
In order to achieve the above object, the fourth invention provides an image processing apparatus comprising:
a first sensor of which main spectral sensitivity characteristic has sensitivity in the vicinity of the main luminescent line of the fluorescent lamp;
a second sensor of which main spectral sensitivity characteristic does not include the main luminescent line of the fluorescent lamp; and
means for obtaining the color rendering of the environment light, on the basis of outputs of the first and second sensors.
Further, an object of a fifth invention is to provide an environment light measurement apparatus which can measure the environment light with simple structure.
In order to achieve the above object, the fifth invention provides the environment light measurement apparatus comprising:
first light detection means of which main spectral sensitivity characteristic has sensitivity in the vicinity of the wavelength 546 nm being the main luminescent line of the fluorescent lamp; and
second light detection means of which main spectral sensitivity characteristic has sensitivity in a wavelength band of 650 nm or longer not including the main luminescent line and in the vicinity of the wavelength 480 nm.
Further, in order to achieve the above object, the fifth invention provides the environment light measurement apparatus comprising:
first light detection means of which main spectral sensitivity characteristic has sensitivity in the vicinity of the wavelength 546 nm being the main luminescent line of the fluorescent lamp;
second light detection means of which main spectral sensitivity characteristic has sensitivity in the wavelength band of 650 nm or longer not including the main luminescent line; and
color temperature measurement means for measuring the color temperature of the environment light.
The above and other objects, features, and advantages of the present invention will be apparent from the detailed description and the appended claims in conjunction with the accompanying drawings.